Air is introduced to combustion chambers of an internal combustion engine through intake passages. The intake air amount is one of parameters reflecting an engine operating state together with an engine rotation speed. An engine control amount according to which the engine operating state is controlled, for example, a fuel injection amount or an ignition timing is set on the basis of the intake air amount. The intake air amount mentioned above is generally determined on the basis of a detection signal from an air flow meter provided in the intake passage.
In recent years, hot wire air flow meters have been mainly used. A hot wire air flow meter has a hot wire and a temperature gauge, which constitute a bridge circuit. The hot wire includes a heat generating resistor which generates heat by a supply of an electric power. The temperature gauge detects a temperature of intake air. In the hot wire air flow meter, when the intake air amount is changed, a heat quantity drawn from the hot wire is changed. The air flow meter determines the intake air amount by utilizing this principle. Specifically, the temperature of the intake air is detected by the temperature gauge mentioned above. The electric power supplied to the hot wire is controlled in such a manner that the temperature of the hot wire is kept higher by a fixed temperature than the detected intake air temperature. The intake air amount is detected on the basis of the change of the electric power at this time.
In recent years, large displacement V engines have been employed in vehicles for the purpose of a further higher power of internal combustion engines. For example, a non-patent document 1 (new model car instruction manual, service manual of TOYOTA Century, April 2000, edited by TOYOTA Motor Corporation, issued by the service division) discloses one example of an engine system in the large displacement V-engine. In this engine system, in order to improve a reduction of pressure loss of the intake air, and a mountability of the internal combustion engine to the vehicle, a part of the intake system is branched into two systems. It becomes easy to enlarge the total flow passage area of the intake passage by branching the intake system, specifically, the intake passage into two systems as mentioned above, and the pressure loss of the intake air flowing within the intake passage is lowered. Further, since this adds to the flexibility of design of the engine, the mountability to the vehicle is improved.
However, in such an intake passage structure that the intake passages of two systems are combined in a downstream side of the intake passage, for example, in an upstream section in the throttle valve, a turbulent flow of the intake air tends to be generated in a section downstream of the combined portion. Accordingly, even if the air flow meter mentioned above is provided in a portion in which the turbulent flow of the intake air tends to be generated, it is hard to obtain an accurate intake air amount. Thus, in the case of the engine system mentioned above, it is unavoidable that an air flow meter that also functions as an intake air temperature sensor be provided in each of the intake passages in a section upstream of the branch position.
In the structure mentioned above, there is a case that the air flow meter is affected by the internal combustion engine main body, which is a heat source, depending on a mounted position. Particularly, during starting of the engine start, there is a high possibility that the air flow meters provided in the respective intake passages, more specifically, the respective intake air temperature sensors detect different intake air temperatures from each other. In this case, there is a risk that it is impossible to obtain the accurate intake air temperature information of the engine system, and moreover, it is hard to achieve a suitable fuel injection amount control with respect to the engine.